I (F31) live with my best friend (M30). Through some research, I have concluded that I might have some attachment issues due to my past and all that. We are extremely close and I have gotten use to spending every night cuddled up on the couch or just hanging out in some way. I even still get a buzz when he asks me if I want to just go to the shops with him.
He has had this FWB for like the last 9 or so months. (I have asked and they agreed to keep it as FWB/casual) Every time she comes over I cant control the attitude I give and I just hide away in my room until she is gone. We have had some conversations about it but I wasn't really sure what I was feeling so I just came up with excuses that might made sense even though he doesn't believe them. I knew it made me anxious but not too sure why. Despite what is probably thought, I don't think it was the romantic aspect. I am happy with how our friendship is. I also think that if he just had a revolving door of girls coming over, it wouldn't bother me. As long as it was just for sex and they were leaving in the morning.
When he goes to her house, it doesn't bother me. Kind of like out of sight, out of mind but when she is here I cant help but feeling like my replacement is being flaunted in my face. She will stay the night and then not leave until 7pm the next night. They are just hanging out, watching TV and chilling.
He recently bought her a PC which triggered me because gaming is something that we do together which is just reinforcing the irrational fear of being forgotten and replaced by someone better.
We are usually pretty good at communication but I don't know if admitting this to him will do any good. Its not like it will or should really change how he goes about things as it is my issue to bare but its also not fair that he cops the attitude and doesn't understand why. Maybe would be more sympathetic when I do just hide away and roll my eyes when he is talking about her.
TLDR: Jealous of my best friends friendship with his FWB. Irrational fear of being replaced.
Will also accept any advice on what I could do to get over it :)